There is continuous development in improving image quality from inkjet printing, as measured by properties such as optical density and mottle. For inks based on aqueous pigment dispersions, optical density can be affected by the rate of pigment aggregation on the substrate. Slow pigment aggregation can lead to poor or average image quality. It has been previously discovered that aggregation can be increased by using pigments capable of binding calcium. Because many papers contain solutes such as Ca2+, Mg2+ and Na+ salts on the surface, the calcium binding pigments can affix to the paper via the salts and enhance the rate of aggregation. For plain and coated papers containing low concentrations of such salts, however, the advantages afforded by calcium binding pigments is lessened.
Accordingly, there remains a need to develop inkjet ink compositions having improved printing performance on a variety of substrates.